The prior art relating to heat-recoverable articles illustrates many different means to effect heating and thereby to recover heat-recoverable articles. These means include hot air, infrared radiation, ultrasonic vibration, chemical exotherm, open flame, and electrical resistance heating. All of these methods suffer from various disadvantages, one of which is insufficient control which either leads to overheated and/or excess temperature conditions which damage the heat-recoverable material, or to under-heated and/or insufficient temperature conditions which result in insufficient recovery of the heat-recoverable article. Other problems occur when the correct temperature is achieved, but the temperature is not maintained at the required level for a sufficient period of time to allow complete or desired recovery of the heat-recoverable article. In one regard, it can be seen that the prior art devices and methods are very energy-inefficient, particularly those in which heat is supplied from an outside source to the outside surfaces of the heat-recoverable article, thereby causing a significant waste of heat and energy. This also limits the applicability of the prior art devices and methods.
Additional problems occur due to non-uniform heating of the mass of the recoverable material in the heat-recoverable article. Thus, in heat-recoverable articles in which the heat-recoverable material is of an even thickness or even mass distribution, the problem has been to obtain uniform or even heating of the heat-recoverable material to assure uniform recovery. In other articles wherein the thickness or mass of the heat-recoverable material differs in various parts of the heat-recoverable article, the problem has been to obtain appropriate heat distribution and sufficient heating in each of the various areas of different thickness or different mass in order to achieve sufficient recovery of the higher mass areas without overheating the areas of lower mass.
Various devices and methods have been attempted in order to auto-regulate or enable an operator to control the heating of heat-recoverable articles. For example, in Glover et al., U.S. Pat. No. 4,228,761, and in DeBlauwe, U.S. Pat. No. 4,450,023, thermochromic coatings are disclosed for visual indicators showing the desired temperature of the article has been attained for sufficient recovery and heating of other materials and components present. However, it should be noted that such indicators provide no means of control or regulation of the heating, but merely provide a visual indication to an operator who can, in turn, control the heating, such as by stopping the application of heat.
Various other attempts have been made to provide a limited amount of heat or to provide self-regulating heating means for heat-recoverable articles. In Deal et al., U.S. Pat. No. 3,551,223, a pyrotechnic coating is disclosed for supplying a specified amount of heat to heat-recoverable articles. In Diaz, U.S. Pat. No. 4,223,209, and Horsma, et al., U.S. Pat. No. 4,654,511, self-regulating conductive polymer heating devices are disclosed for use with heat-recoverable articles.
These and other devices and methods for providing controllable or self-regulating, properly proportioned heating for heat-recoverable articles have not produced satisfactory results for a number of reasons. A primary cause of the problems and difficulties in achieving the proper or desired control of temperature and the desired proportioning of heating is due to the fact that as the heat-recoverable article recovers, the shape, dimensions, geometry, thickness, and other physical characteristics of the heat-recoverable article change drastically--and in many cases change non-uniformly over the different parts and areas of the heat-recoverable article.
In addition, the geometric problems are further complicated by the fact that the geometry is constantly changing while the recovery of the article is occurring. Consequently, the thermochromic coating indicators are frequently inadequate to indicate whether the desired temperature or heating has been achieved in particular areas of the article. In thick walled atricles the thermochromic coating only indicates the surface temperature and does not indicate the internal temperature of the article. Also, erroneous or inadequate indications are given when hot air or open flame is used, because the coating is heated first Similarly, the changing geometry and configuration of heat-recoverable articles as they recover results in various complications and problems associated with the use of the above-mentioned self-regulating conductive polymer heating elements.
A number of the above disadvantages have been overcome by Derbyshire. As disclosed by Derbyshire in co-pending U.S. patent application Ser. No. 445,819 filed Dec. 1, 1982 and corresponding to PCT International Publication WO84/02098 (Application No. PCT/US83/01851), it has been found to be advantageous to use Curie temperature limited heating for various heat-recoverable articles. Derbyshire discloses the use of ferromagnetic materials having the desired Curie temperature in electrically conductive layers to provide auto-regulated heating to the Curie temperature of the material upon application of an alternating current to the conductive layer of ferromagnetic material. The power applied to the ferromagnetic layer is in the form of an alternating current source which produces skin effect or eddy current heating in the continuous ferromagnetic layer. As the ferromagnetic layer reaches the Curie temperature, the permeability of the layer drops and the skin depth increases, thereby spreading the current through the wider area of the ferromagnetic layer until the Curie temperature is achieved throughout and the desired heating is achieved. The alternating current is supplied to the ferromagnetic layer either directly from a power source through electrodes in the conductive layer of ferromagnetic material or is supplied inductively from an adjacent insulated conductive layer directly powered with the alternating current.
While the Derbyshire type of Curie temperature limited heating of heat-recoverable materials and articles provides certain advantages and improvements over other prior art, the Derbyshire skin effect or eddy current heating has one aspect which is a disadvantage in many applications. The disadvantage is due to the necessity of their being electrically conductive layers in the heat-recoverable articles. In many applications, it is desirable to have no electrically conductive layers or areas in the heat-recoverable article.
The disclosures of the above references are incorporated herein by reference.
In view of the insufficiencies and certain disadvantages of the above prior art devices and articles, it is apparent that there is a need for improved auto-regulating, heat-recoverable articles. The present invention has been developed to provide auto-regulating, heat-recoverable articles as well as systems for using those articles which do not suffer from the insufficiencies or disadvantages mentioned above.
Therefore, it is an object of this invention to provide heat-recoverable articles which do not require hot air, infrared radiation, ultrasonic vibration, flame, or D.C. resistance heating to effect recovery.
It is a further object of this invention to provide heat-recoverable articles which are auto-regulating and thereby are protected from overheating.
It is a further object of this invention to provide heat-recoverable articles which can be electrically non-conductive in their entirety or in any desired portion thereof.
It is another object of this invention to provide heat-recoverable articles which are capable of minimizing the energy requirements necessary for recovery.
It is another object of this invention to provide improved Curie temperature limited heating for heat-recoverable articles by eliminating the need for direct electrical connection to the heat-recoverable article.
It is another object of this invention to permit easy selection of precise Curie temperature limited heatable articles and to tailor the Curie temperature to particular needs without concern for incorporating electrically conductive layers or electrical connections in the article.
It is another object of this invention to provide an improved self-heating soldering device incorporating a self-heating, heat-recoverable sleeve with a solder preform located inside the sleeve.
It is another object of this invention to provide an improved heat-recoverable article incorporating a fusing material, such as solder, or a thermoplastic material within a tubular member which is auto-regulating at a Curie transition temperature which is above the activation temperature of the fusing material, above the recovery temperature of the heat-recoverable material, and is below the degradation temperature of those materials.
These and other objects are achieved by the present invention as will be recognized by one skilled in the art from the following summary and description of this invention.